To allow a cathode-ray tube to have an ability to swiftly transfer the electricity generated by the static induction caused by the a turning on or off of a switch, to ground, i.e. an antistatic property and to provide high image contrast, has been proposed a method to form a colored transparent electroconductive film on the face plate of a cathode-ray tube in Japanese Patent Application No. 1-145325. That is, it has been proposed to coat a colored transparent electroconductive film, on an outer surface of the face plate of cathode-ray tube, by an alcohol solution containing one or more organic dyes, at least one electroconductive metal oxide selected from tin oxide (SnO.sub.2), indium oxide (In.sub.2 O.sub.3), and antimony oxide (Sb.sub.2 O.sub.3), and ethyl silicate, and to heat and dry the surface at a temperature of about 100.degree.-200.degree. C.
In the above proposed method, the alcohol solution firstly prepared by firstly preparing a solution consisting of at least one metal oxide selected from SnO.sub.2, In.sub.2 O.sub.3 and Sb.sub.2 O.sub.3, ethyl silicate capable of forming a silica gel when subjected to hydrolysis and then to dehydration-condensation, a mixed solution consisting of alcohols, ketones or the like, water and an acid catalyst, and then adding thereto at least one organic dye capable of providing desired optical properties, selected from azo dyes, anthraquinone dyes and the like, with the coating of the alcohol solution being carried out by any of spin coating, dip coating and spray coating.
The above proposed method has a number of problems, namely, the colored transparent electroconductive film may exhibit desired light absorption when it contains one or more organic dye in an amount as small as 1% by weight or less, and may give high image contrast; however, the film tends to show earlier color fading when exposed to water, an acid, an alkali, an organic solvent or, the like. The film shows color fading in about one hour particularly at high temperatures, for example, when placed in a boiling water. Since it is anticipated that electric appliances using the film may be subjected to high temperatures and high humidity during the storage, marine transportation, etc., it has been required to improve the water resistance and chemical resistance of the film.
Another problem resides in the fact that when a solution for formation of a colored transparent electroconductive film is coated on the face plate and subsequently or simultaneously therewith a solution for formation of a non-glare surface protective layer composed mainly of an alcohol solution containing ethyl silicate is coated on the surface-coated face plate, the color dye or other components in the colored transparent electro-conductive film dissolves in and spreads into the non-glare surface protective layer because the surface of the film is unstable and active.
Since the solution for formation of a non-glare surface protective layer contains large amounts of an alcohol, water, etc. and has a low viscosity, the solution tends to dissolve the dye, etc. present in the colored transparent electroconductive film. When there is such dissolution, the dye is removed when the surface of cathode-ray tube is cleaned with a solvent, thereby resulting in a deterioration in the optical properties of the cathode-ray tube.
Furthermore, the conventionally used organic dyes used are not sufficient in chemical and optical durabilities and need improvement.